title: Experimental model to evaluate the effect of hydrothorax and lobar resection on lung compliance.
abstract: OBJECTIVE
  The objective of this study was to evaluate to what extent lung compliance is affected by the individual and combined action of lung resection and hydrothorax in an animal model.
  
  
  METHODS
  Anaesthetized and mechanically ventilated rabbits (weight range 2 ÷ 2.2 kg) were randomized in two groups: (i) experimental hydrothorax (from 2 to 8 ml) (n = 5) and (ii) right lower lobe lobectomy (n = 4) and right middle plus lower lobe resection (n = 2). To obtain lung compliance, we measured alveolar, oesophageal pressures and lung volume during slow inflation manoeuvres in control conditions and after hydrothorax or lung resection. Lung compliance was estimated as the change in lung volume divided by the change in transpulmonary pressure. Based on the changes in compliance of the whole lung, we calculated the corresponding changes in compliance of the right lung, which was directly exposed to unilateral hydrothorax and lobectomy.
  
  
  RESULTS
  Average total lung compliance in the control was 3.3 ± 0.8 (SD) ml/cmH2O. Eight millilitres of hydrothorax significantly decreased (P < 0.001) lung compliance to 2.7 ± 0.7 ml/cmH2O and increased pleural liquid pressure at the bottom of the cavity from -1 cmH2O up to ∼ 2.5-3 cmH2O. Resection of the right lower lobe significantly decreased (P < 0.001) lung compliance to 1.75 ± 0.3 ml/cmH2O. Resection of the right middle plus lower lobes significantly decreased (P < 0.001) lung compliance to 1.52 ± 0.4 ml/cmH2O.
  
  
  CONCLUSIONS
  Following hydrothorax, the decrease in right lung compliance (∼ 45%) was much greater than that expected based on the estimated decrease in right lung volume (20%). We attribute this difference to the fact that hydrothorax causes the lung to be exposed to positive, rather than sub-atmospheric, pressure, causing atelectasis. Following lobectomy, right lung compliance decreased by 62 and 80% for estimated decreases in lung volume of 30 and 60%. This difference could reflect inaccuracy in the estimate of lung volume reduction based on resected weight and/or surgical damage. We conclude that potential detrimental effects of hydrothorax and lobar resection decrease lung compliance and expose the lung to the risk of over-distension when a chest drain is applied.
authors.affiliation: Tbm Lab, Dipartimento di Elettronica, Informazione e Bioingegneria, Politecnico di Milano, Milano, Italy.
authors.forename: Caterina
authors.initials: C
authors.lastname: Salito
authors.forename: Dario
authors.initials: D
authors.lastname: Bovio
authors.forename: Enrico
authors.initials: E
authors.lastname: Mazzuca
authors.forename: Ilaria
authors.initials: I
authors.lastname: Rivolta
authors.forename: Alessandro
authors.initials: A
authors.lastname: Brunelli
authors.forename: Andrea
authors.initials: A
authors.lastname: Aliverti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Miserocchi
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena / Q000502:physiology; D004195:Disease Models, Animal; D006876:Hydrothorax / Q000503:physiopathology*; D008168:Lung / Q000503:physiopathology* / Q000601:surgery*; D008170:Lung Compliance / Q000502:physiology*; D008297:Male; D011013:Pneumonectomy; D011312:Pressure; D011817:Rabbits
keywords: Air leak; Idiopatic lung oedema; Lung over-distension